Barbed suture having increased holding strength

ABSTRACT

A wound closure device having a filamentary element having a proximal end and a distal end, and a stop element coupled thereto and having a leading edge area defined by thickness and a width and having a total surface area. The leading edge area is substantially perpendicular to a longitudinal axis of the filamentary element. The device may have a ratio of the leading edge area to the total surface area that is less than 10%, a ratio of the length to the maximum thickness of the stop element that is at least 4, or a ratio of the length to the width of the stop element is at least 1 for any given thickness.

FIELD OF THE INVENTION

The present invention relates generally to the field of medical devices,and more particularly to barbed suture devices having increased holdingstrength.

BACKGROUND

Many wound and surgical incisions are closed using surgical sutures orsome other surgical closure device. Barbed sutures are well known andhave recently been gaining attention for various medical applications.Typically, barbed sutures are constructed with a series of “barbs” or“protrusions” (used interchangeably herein) that extend outwardly fromthe suture, and function to increase the holding strength of the sutureand/or eliminate the need for knot tying. The size and shape of thebarbs have practical limitations in a surgical setting, and cannotsimply be increased wherever increased holding strength is desired.

Some sutures and barbed sutures have been known to include anchors, tabsor the like on the distal end of the suture to provide a “stop” at theend that increases the holding strength of the suture and eliminates theneed to tie knots to secure the suture. Conventional thinking dictatesthat the larger the surface area of the stop in a directionperpendicular to the direction of insertion of the suture, the moreholding strength that will be achieved. Again, there are practicallimitations on size however, as large masses may be intolerable insurgical procedures and/or palpable and therefore undesirable. Further,with T-shaped stops, the perpendicular portion is structurally weak whena bending moment is applied as it would be when pulling on the suture toapproximate a wound.

Therefore, there remains a need to enhance the holding strength of asurgical suture without significantly increasing the insertion force,stiffness of the suture, or palpability of the device.

SUMMARY OF THE INVENTION

The present invention provides a wound closure device including afilamentary element having a proximal end and a distal end, a stopelement coupled to the distal end of the filamentary element and havinga leading edge area defined by thickness and a width, and a totalsurface area. The leading edge area faces substantially perpendicular toa longitudinal axis of the filamentary element, and the ratio of theleading edge area to the total surface area is less than 10%. Accordingto one embodiment, the ratio is less than 5%.

According to various embodiments, the width of the stop element may begreater than 70 mils, the length of the stop element may be greater than70 mils, and/or the maximum thickness of said stop element may bebetween 6 and 25 mils.

According to one embodiment, the thickness of the stop element varies,and/or a minimum thickness of the stop element may be between 4 and 12mils. According to yet another embodiment, the leading edge thicknessincludes a maximum thickness at a center and/or at first and/or secondouter edges, and a minimum thickness at a location between the centerand the first outer edge and between the center and the second outeredge.

In yet another embodiment, the wound closure device further includes aplurality of projections extending outwardly from the filamentaryelement along at least a portion of its length. The plurality ofprojections may extend outwardly from said filamentary element byapproximately 6-25 mils.

The device may be made of a polymeric, metallic or ceramic material thatare absorbable or non-absorbable. In yet another embodiment, the deviceis made of a polymer material selected from the group consisting ofabsorbable and non-absorbable homopolymers, random copolymers, blockcopolymers or blends made from polydioxanone, polyglactin, polyglycolicacid, copolymers of glycolide, lactide, and/or caprolactone,polyoxaesters, poliglecaprone, polypropylene, polyethylene,polyvinylidene fluoride (PVDF), hexafluoropropylene, copolymers ofvinylidene fluoride and hexafluoropropylene, polyesters, polyethyleneterephthalate, polybutylene terephthalate, glycol-modified polyethyleneterephthalate, polytetrafluoroethylene, fluoropolymers, thermoplasticelastomers, ionomers, copolymers of ethylene and methacrylic acid,polyamides, polytetramethylene oxide, polystyrene, polybutadiene,polybutylene, etc. including combinations and/or copolymers ofabsorbable and non-absorbable materials.

According to yet another embodiment, a ratio of the length to maximumthickness of the stop element is greater than 4.

In yet another embodiment, the maximum thickness of the stop isapproximately 8-25 mils, the width of the stop is approximately 70-120mils, and the length of the stop is approximately 39-200 mils.

The present invention also provides a wound closure device including afilamentary element extending along a longitudinal axis between aproximal end and a distal end, and a stop element coupled to the distalend of the filamentary element and that has a length extendingsubstantially parallel to the longitudinal axis of the filamentaryelement, a width extending substantially perpendicular to saidlongitudinal axis, and a maximum thickness. The ratio of the length tothe maximum thickness of the stop element is at least 4.

In alternate embodiments, the maximum thickness of the stop element isbetween 8 and 25 mils, the length of the stop element is greater than 39mils, and/or the width of the stop element is between 70 and 120 mils.

In yet another embodiment, the wound closure device further includes aplurality of projections extending outwardly from the filamentaryelement along at least a portion of its length.

In yet another embodiment, the thickness of the stop element varies, andin another particular embodiment, the leading edge thickness includes amaximum thickness at a center and/or at first and/or second outer edges,and a minimum thickness at a location between the center and the firstouter edge and between the center and the second outer edge.

Also provided is a wound closure device including a filamentary elementextending along a longitudinal axis between a proximal end and a distalend, and a stop element coupled to the distal end of the filamentaryelement. The stop element has a length extending substantially parallelto the longitudinal axis of the filamentary element, a width extendingsubstantially perpendicular to said longitudinal axis, and a maximumthickness, and for any given maximum thickness of the stop element, theratio of the length to the width of the stop element is at least 1.

In a further embodiment, the ratio of the length to the width of thestop element is at least 1.5.

These and other objects, features and advantages of the presentinvention will be apparent from the following detailed description ofillustrative embodiments thereof, which is to be read in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wound closure device according to the presentinvention including an insertion needle;

FIG. 2 is an enlarged view of the distal end of the wound closure deviceof FIG. 1;

FIG. 3 is a top view of the stop element of the wound closure device ofFIG. 1;

FIG. 4 is a side view of the stop element of the wound closure device ofFIG. 1;

FIG. 5 is a cross-sectional view of the leading edge of the stop elementof the wound closure device of FIG. 1;

FIG. 6 is a graph illustrating the holding strength of fixation tabs ofequal leading edge maximum thickness and width, but with varying length;

FIG. 7 is a graph illustrating elongation of a fixation tab as afunction of length to width ratio for a given maximum thickness;

FIG. 8 is a graph illustrating a load-extension curve for a fixation tablength to width ratio of 0.5; and

FIG. 9 is a graph illustrating a load-extension curve for a fixation tablength to width ratio of 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of a wound closure device 100according to the present invention. The wound closure device 100includes a filamentary element 102 comprised of any suitable surgicalsuture material (i.e., absorbable and non-absorbable polymericmaterials, metallic, or ceramic materials) that preferably includes aplurality of barbs 104 that extend outwardly therefrom. The suture maybe formed by any suitable method, but preferably is compound profilepunched from preformed material in a manner described in more detail inU.S. Patent Publication No. 2007/0257395, which is incorporated hereinby reference in its entirety. The proximal end 109 of the wound closuredevice may include a needle or other insertion device 101. At the distalend 106 of the wound closure device is a fixation tab or stop element orthe like 108. The stop 108 has a leading edge 110 defined by a leadingedge thickness t and a leading edge width w, and also has a length l asshown in FIGS. 3-5. As indicated previously, known T-shapedconfigurations have relatively weak stiffness when a bending moment isapplied, such as when tension is applied to the suture to approximate awound. The graph depicted in FIG. 6 more clearly illustrates theadvantage of the present invention over a T-shaped end configuration.Fixation tabs of equal leading edge maximum thickness (t) and width (w)(leading edge area), but varying length (l) were made and the holdingstrength tested. The holding strength was tested by passing the barbedsuture through a porcine abdominal wall fascia sample and pullingagainst the fixation tab until failure occurred either by the stopbreaking in some fashion, the stop pulling through the tissue, or acombination of both. The maximum load prior to failure was recorded andillustrated in FIG. 6.

As shown therein, the holding strength decreases as the geometry becomesmore like a T-shaped member, or in other words, as the ratio of lengthto leading edge area or length to maximum thickness decreases. Theholding strength can be increased by increasing the thickness or widthof the stop, but as indicated previously, there are practical andclinical limitations on the size and mass that can be implanted.

In addition to the length to maximum thickness or leading edge arearatio, the length l to width w ratio is also a significant considerationfor any given maximum thickness. Surprisingly and counter-intuitively, aratio of at least 1:1 provides much increased holding strength. FIG. 7illustrates the elongation of the fixation stop or tab as a function ofthe length to width ratio for a given maximum thickness. As shown, thepercentage of elongation (or more simply the amount of deformation)required to reach catastrophic failure increases with increasing lengthto width ratio.

In addition to raw elongation percentages, the actual amount of energyrequired for the failure of the device increases with increasing lengthto width ratios. This is illustrated by FIGS. 8 and 9, in which the areaunder the load-extension curve is a measure of the strain energy untilcatastrophic failure. As the length to width ratio increases, the amountof strain energy required to reach catastrophic failure significantlyincreases. FIG. 8 illustrates a load-extension curve for a fixation tabhaving a length to width ratio of 0.5:1. As illustrated, the devicereaches a peak load then decreases dramatically with sudden failure.FIG. 9 illustrates a load-extension curve for a fixation tab having alength to width ratio of 2:1. As illustrated, the curve has a secondpeak, and much greater extension before catastrophic failure occurs. Inother words, the strain energy significantly increases as the length towidth ratio increases from 0.5 to 2.

Referring once again to FIGS. 3-5, the leading edge area of the stopelement has relatively little surface area in contact with tissue whenthe suture is under tension, but its ratio of length l to maximumthickness t is very large. Thus, the actual area in contact with tissue(leading edge area 110) in the direction of load is very small relativeto the overall dimensions of the fixation stop or tab. This relativelylong length, but minimal thickness allows the stop to be placed in thewound in a relatively flat position, which minimizes palpability andallows the opposing sides of the tissue to neatly cover the stop. Sincethe stop lies nicely in the tissue, it can be placed at the apex of thewound, lateral to one side of the wound etc, without impeding thesurgeon's individual closure technique.

In a preferred embodiment, the leading edge relative to the totalsurface area of the stop (sum of surface area of all sides) is small,preferably less than 10% and more preferably less than 5%. This iscounterintuitive, as conventional thinking dictates that in order toincrease holding strength and/or minimize failure, one must increase ormaximize the surface area under load in order to spread out the load anddecrease the load per unit area. The relatively long length l, butminimal thickness t results in clinical advantages, including flatpositioning that minimizes palpability, and versatile positioning asmentioned above.

According to a preferred embodiment shown in detail in thecross-sectional view of FIG. 5, the leading edge area of the stop of thepresent invention preferably is not rectangular, but rather has athickness that varies across its width. The preferred stop 108 has amaximum thickness t at its outer edges 120 and center 122, and a minimumthickness t₂ at points between the center and outer edges. In thisembodiment, the filamentary element has a filament width f ofapproximately 5-25 mils, and the barbs 104 extend outwardly therefrom bya distance d of approximately 6-25 mils. The stop has a length l of atleast 39 mils, preferably 100 to 200 mils, and a width of greater than70 mils, more preferably greater than 90 mils, and most preferablygreater than 95 mils. Further, the maximum thickness t is greater than 6mils, and preferably between 10 and 25 mils, and the minimum thicknesst₂ is less than 15 mils, but preferably between approximately 5 and 9mils. The length to maximum thickness ratio is preferably greater than4, and the length to minimum thickness is preferably greater than 9.Finally, the length to width ratio is greater than 1, and preferablygreater than 1.5.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments and that various other changes and modifications may beeffected herein by one skilled in the art without departing from thescope or spirit of the invention.

What is claimed is:
 1. A surgical suture adapted to approximate opposingtissue surfaces without knot tying, the surgical suture having a firstend and a second end comprising: a filamentary element having a proximalend and a distal end, a plurality of barbs extending outwardly therefromso as to allow movement of the surgical suture through tissue in a firstdirection toward the proximal end of the filamentary element and firstend of the surgical suture and resist movement in a second oppositedirection; a stop element having a total surface area and asubstantially planar leading edge area defined by thickness and a width,wherein the stop element is coupled to the distal end of the filamentaryelement so that the leading edge area is substantially perpendicular toa longitudinal axis of the filamentary element and faces the first endof the surgical suture and lies substantially within a first plane, thestop element also having a length extending in the direction of thelongitudinal axis of the filamentary element that is greater than thewidth, the stop element adapted to resist movement of the surgicalsuture in said first direction; wherein a ratio of the leading edge areato the total surface area is less than 10%, and wherein the filamentaryelement and stop element are comprised of the same polymeric material.2. The surgical suture according to claim 1, wherein the ratio of theleading edge area to the total surface area is less than 5%.
 3. Thesurgical suture according to claim 1, wherein the width of the stopelement is greater than 70 mils.
 4. The surgical suture according toclaim 3, wherein a length of the stop element is greater than 70 mils.5. The surgical suture according to claim 1, wherein a maximum thicknessof said stop element is between 6 and 25 mils.
 6. The surgical sutureaccording to claim 1, wherein the thickness of the stop element varies.7. The surgical suture according to claim 6, wherein a minimum thicknessof the stop element is between 4 and 12 mils.
 8. The surgical sutureaccording to claim 6, wherein the leading edge thickness includes amaximum thickness at a center and/or at first and/or second outer edges,and a minimum thickness at a location between the center and the firstouter edge and between the center and the second outer edge.
 9. Thesurgical suture according to claim 1, further comprising a plurality ofprojections extending outwardly from the filamentary element along atleast a portion of its length.
 10. The surgical suture according toclaim 9, wherein said plurality of projections extending outwardly fromsaid filamentary element by approximately 6-25 mils.
 11. The surgicalsuture according to claim 1, wherein the polymeric is absorbable ornon-absorbable.
 12. The surgical suture according to claim 11, whereinthe polymeric material selected from the group consisting of absorbableand non-absorbable homopolymers, random copolymers, block copolymers orblends made from polydioxanone, polyglactin, polyglycolic acid,copolymers of glycolide, lactide, and/or caprolactone, polyoxaesters,poliglecaprone, polypropylene, polyethylene, polyvinylidene fluoride(PVDF), hexafluoropropylene, copolymers of vinylidene fluoride andhexafluoropropylene, polyesters, polyethylene terephthalate,polybutylene terephthalate, glycol-modified polyethylene terephthalate,polytetrafluoroethylene, fluoropolymers, thermoplastic elastomers,ionomers, copolymers of ethylene and methacrylic acid, polyamides,polytetramethylene oxide, polystyrene, polybutadiene, polybutylene, etc.including combinations and/or copolymers of absorbable andnon-absorbable materials.
 13. The surgical suture according to claim 1,wherein a ratio of a length to maximum thickness of the stop element isgreater than
 4. 14. The surgical suture according to claim 1, wherein amaximum thickness of the stop is approximately 8-25 mils, the width ofthe stop element is approximately 70-120 mils, and a length of the stopelement is approximately 39-200 mils.
 15. A surgical suture adapted toapproximate opposing tissue surfaces without knot tying comprising: afilamentary element extending along a longitudinal axis between aproximal end and a distal end, and having a plurality of barbs extendingoutwardly therefrom so as to allow movement of the surgical suturethrough tissue in a first direction toward the proximal end of thefilamentary element and resist movement in a second opposite direction;a stop element having a length extending substantially parallel to thelongitudinal axis of the filamentary element, and having a substantiallyplanar leading edge area extending substantially perpendicular to saidlongitudinal axis and defined by a width and a maximum thickness, theleading edge area being fixedly coupled to the distal end of thefilamentary element along said leading edge area; wherein the ratio ofthe length to the maximum thickness of the stop element is at least 4.16. The surgical suture according to claim 15, wherein the maximumthickness of the stop element is between 8 and 25 mils.
 17. The surgicalsuture according to claim 16, wherein the length of the stop element isgreater than 39 mils.
 18. The surgical suture according to claim 17,wherein the width of the stop element is between 70 and 120 mils. 19.The surgical suture according to claim 17, further comprising aplurality of projections extending outwardly from the filamentaryelement along at least a portion of its length.
 20. The surgical sutureaccording to claim 17, wherein a thickness of the stop element varies.21. The surgical suture according to claim 20, wherein a leading edge ofthe stop element includes a maximum thickness at a center and/or atfirst and/or second outer edges, and a minimum thickness at a locationbetween the center and the first outer edge and between the center andthe second outer edge.